The purpose of this project is to first study the osmotic behavior of perfused tissues and organs during the introduction and removal of cryoprotective agents (CPAs) and then to develop optimum CPA introduction and removal protocols. Currently, scientists at the MRC Medical Cryobiology Group at Cambridge University are experimentally monitoring the overall weight and venous outflow of rabbit kidneys perfused with solutions containing different types and concentrations of CPAs. At NIH, these data are being used in conjuction with a previously developed non-steady state mass transport model to deduce the permeability and elastic properties of the perfused kidneys. Continual comparison of the theoretical predictions of organ behavior during CPA introduction/removal with the experimental observations of the responses of perfused organs to changes in the composition of their perfusates hopefully will facilitate the development of optimum CPA introduction and removal protocol.